A major way that trauma kills people is by breaking blood vessels and causing hemorrhage. The body is naturally able to overcome some amount of damage to blood vessels through blood clotting. Blood clotting occurs because of a number of enzymes which act in a cascade in response to damage to blood vessel walls or blood itself. Often, however, seriously injured people bleed too profusely for natural clotting to be able to stabilize their bleeding. A cycle can occur in which traumatic injury and blood loss produce acidosis and hypothermia, which in turn weaken the blood's ability to clot because of their effect on the reactions and enzymes that carry out blood clotting. There has consequently been research on ways to accelerate and facilitate the natural process of blood clotting.
U.S. Pat. No. 4,822,349 to Hursey et al. proposed the use of zeolite crystals in contact with blood to facilitate clotting. The mechanism suggested there was that the zeolite crystals would adsorb water from blood. It is known that zeolites have a large ability to absorb water, in part because they have a large surface area accessible to water molecules. It is also indicated in the Hursey et al. '349 patent that the heat generated by the exothermic reaction between zeolite material and moist blood would cauterize the wound.
U.S. Patent Publication No. 2003/0133990 to Hursey et al. made further proposals for the use of zeolite crystals in combination with other agents to facilitate clotting. A commercial zeolite-containing clotting accelerator called QuikClot (Z-Medica, Wallingford, Conn.) received FDA approval in 2002. QuikClot is a dehydrated powder comprised of a zeolite with the FAU topology and other inorganic solids. There have been various reports of experience with QuikClot.
It has been discovered that the use of QuikClot results in a temperature increase which may be problematic. For example, in James K. Wright et al., J. Trauma, 57, 224-30 (2004), it was reported that in experiments with anesthetized pigs, “[a]pplication of the agent [QuikClot] resulted in elevated tissue surface temperatures in excess of 95° C. and internal tissue temperatures exceeding 50° C., 3 mm deep to the bleeding surface.” This effect is believed to be due to the fact that the adsorption of water onto zeolites is an exothermic process. For example, for zeolite A the enthalpy of adsorption has been reported to be on the order of −100 kJ/mol. Tsutsumi et al., Colloid Polymer Sci., 277, 83-88 (1999).
As a way of dealing with the problem of heat release from products of the QuikClot type, it has been proposed to control the degree of hydration of the zeolite prior to applying it to tissue. This results in a lower degree of water absorption, which in turn limits the amount of heat generated. See in this regard U.S. Published Patent Application No. 2005/0058721.
There is therefore a need for a blood clotting accelerator which has the advantage of high adsorption of water achieved by the use of zeolites, but which does not release as much heat as zeolites do.